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Full text of "Text Book Of Mechanical Engineering"

Appendix II.

913

r

4*3.     Fig.  875   shews  the  engine,   whose  only objection   was
complication and weight of parts.

Self-starter.—There are three methods of starting a gas
engine: (i) by turning round during four strokes, igniting, and
keeping moving for a short time, (2) by the use of a small
turning engine for large examples, (3) by attaching a c self-
starter ' to carry the piston through four strokes. In Lanchester's-
apparatus, Fig. 876, the exhaust-valve A is held up during
expansion and compression by a special earn, which slips out
of gear after starting; while B is a cock for admitting gas, and c is
open for the escape of gas and air, the mixture being lit by the
flame E. Having placed the crank past dead-centre, the flame c
is watched: at first it is blue, then brighter, and just as it begins-

Fig- 876.

to roar, B is closed, which causes the flame to strike back into
the cylinder and explode the charge, non-return valve D lifting
automatically to prevent escape. This impulse should carry the
piston through four strokes, and very little aid continue the
motion.

For engines of 8 or 10 H.P. gas is most conveniently obtained
from company's mains, but for larger engines a special plant for
cheap gas is advisable. • There are two methods of procuring gas
from solid fuel: (i) by distillation in retorts and subsequent
purification, (2) by combustion. The latter may be practised
in two ways. Producer gas is obtained by burning coke to form
CO, the air supply being restricted. Water gas is made by
burning coke to incandescence and then 'directing a jet of steam